This application claims the priority of Korean Patent Application No. 2003-81724, filed on Nov. 18, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a fingerprint sensor and a fabrication method thereof, and more particularly, to a fingerprint sensor adopting a complementary metal-oxide semiconductor (CMOS) structure on which a piezoelectric region for generating ultrasonic waves is formed, so as to be fabricated using a simple process and to authenticate a fingerprint at a high speed.
2. Description of the Related Art
In the past, goods were purchased through off-line direct trades by cash payments. However, economic and social advances have changed this way of trade into today's transactions by credit cards, off-line e-money, or the like. This gives rise to a social problem of security management of personal information. Thus, a process of inputting identifications (IDs) and passwords is not sufficient to secure personal information.
Accordingly, personal information must be reliably secured. Also, in order to provide portable or personal information at any place, a specific signal must be sensed and deciphered to establish a user's identity in-situ. A security system generally adopts a personal authentication method using biometric technology, i.e., fingerprint sensing technology. A fingerprint sensing system includes a fingerprint scanner, i.e., a fingerprint sensor, and a signal processing algorithm. The fingerprint sensing system must have a high sensing rate and a low error rate to obtain a high-quality image of a fingerprint. A high-performance fingerprint sensor is necessary for this high-quality image of the fingerprint.
A fingerprint sensor is generally classified as an optical type sensor, a capacitive type sensor, an ultrasonic type sensor, and the like. The optical type of fingerprint sensor is convenient to use but is relatively high-priced, sensitive to the dry or moist state of the fingerprint part of a finger to cause inexact fingerprint sensing, and may sense a false fingerprint as a true fingerprint. The capacitive type fingerprint sensor is lower priced than the optical type fingerprint sensor, compact, and highly stable but sensitive to the dry or moist state of the fingerprint part of the finger. In contrast, the ultrasonic type fingerprint sensor can obtain reliable sensing results regardless of the state of the fingerprint part of the finger.
An ultrasonic type fingerprint sensing system generally follows a fingerprint authentication process shown in FIG. 1A. First, the ultrasonic type fingerprint sensing system senses a fingerprint using a fingerprint sensor, extracts a characteristic portion from the sensed fingerprint, and stores the characteristic portion in a database (DB) to be used to distinguish the fingerprint from different types of fingerprints. Thereafter, the ultrasonic type fingerprint sensing system compares a characteristic portion of a fingerprint obtained during fingerprint authentication with the characteristic portion of the fingerprint stored in the DB to authenticate the obtained fingerprint.
FIG. 1B is a cross-sectional view of an ultrasonic type fingerprint sensor disclosed in U.S. Pat. No. 5,587,533. In the ultrasonic type fingerprint sensor of FIG. 1B, an ultrasonic transducer 140, a mirror 156, a motor 160, an actuator 154, and a signal processor (not shown) are separately fabricated and then put together. Thus, the ultrasonic type fingerprint sensor adopts a separately fabricated probe 102, which scans a fingerprint, and thus is costly and not easily applied to portable terminals. Also, the ultrasonic type fingerprint sensor obtains an image of a fingerprint using a scan method, resulting in slow fingerprint authentication.